@article{wang_wee_peters_2022, title={Amplification of Lamb-Wave Detection via Fiber Bragg Gratings Using Ultrasonic Horns}, volume={5}, ISSN={["2572-3898"]}, DOI={10.1115/1.4053582}, abstractNote={Abstract
               Fiber Bragg grating (FBG) sensors are often applied as Lamb wave detectors for structural health monitoring (SHM) systems. Analyzing the measured signal for the identification of structural damage requires a high signal-to-noise ratio (SNR) because of the low-amplitude Lamb waves. This paper applies a two-dimensional ultrasonic horn between the structure and a remotely bonded FBG sensor to increase the amplitudes of the measured signal. Experimentally we test a variety of ultrasonic geometries and demonstrate a 100% increase in the measured ultrasonic signal amplitude using a metallic ultrasonic horn with step-down geometry. A bonding procedure for the combined ultrasonic horn and optical fiber is also developed that produces repeatable signal measurements. For some horn geometries, an additional vibration signal at the Lamb wave excitation frequency is observed in the measurements. Laser Doppler vibrometry (LDV) measurements and finite element analysis demonstrate that the signal is due to the natural vibration of the horn. The experimental results demonstrate that using an aluminum ultrasonic horn to focus wave is an excellent method to increase the sensitivity of the FBG to the small amplitude Lamb wave, provided the horn vibration characteristics are taken account in the design of the measurement system.}, number={3}, journal={JOURNAL OF NONDESTRUCTIVE EVALUATION, DIAGNOSTICS AND PROGNOSTICS OF ENGINEERING SYSTEMS}, author={Wang, Chia-Fu and Wee, Junghyun and Peters, Kara}, year={2022}, month={Aug} }
 @article{wang_wee_peters_2022, title={Amplifying Lamb Wave Detection for Fiber Bragg Grating with a Phononic Crystal GRIN Lens Waveguide}, volume={22}, ISSN={["1424-8220"]}, url={https://www.mdpi.com/1424-8220/22/21/8426}, DOI={10.3390/s22218426}, abstractNote={This paper demonstrates that a graded-index (GRIN) phononic lens, combined with a channel waveguide, can focus anti-symmetric Lamb waves for extraction by a detector with strong directional sensitivity. Guided ultrasonic wave inspection is commonly applied for structural health monitoring applications; however, obtaining sufficient signal amplitude is a challenge. In addition, fiber Bragg grating (FBG) sensors have strong directional sensitivity. We fabricate the GRIN structure, followed by a channel waveguide starting at the focal point, using a commercial 3D printer and mount it on a thin aluminum plate. We characterize the focusing of the A0 mode Lamb wave in the plate, traveling across the GRIN lens using 3D laser Doppler vibrometry. We also measure the extraction of focused energy using an FBG sensor, examining the optimal sensor bond location and bond length in the channel of the waveguide for maximum signal extraction. The measured amplification of the ultrasound signal is compared to theoretical predictions. The results demonstrate that significant amplification of the waveform is achieved and that selecting the location of the FBG sensor in the channel is critical to optimizing the amplification.}, number={21}, journal={SENSORS}, author={Wang, Chia-Fu and Wee, Junghyun and Peters, Kara}, year={2022}, month={Nov} }